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This is a paragraph from a tutorial i've read
Next, we calculate the refraction. If you remember your highschool physics, you know that:
refraction index = sin( angle of incoming light ) / sin( angle of refracted light )
so that the angle of the refracted beam can be calculated like this:
angle of refracted light = arcsin( sin( angle of incoming light ) / refraction index )
where the refraction index is that of water: 1.33.
Third, we need to calculate where the refracted beam hits the image, or its relative position to the place where the incoming light beam originally entered:
displacement = tan( angle of refracted beam ) * height difference
Could you tell me how is the displacement computed,i can't understand it.[looksaround]
Thanks!

"a" is the angle between the light source and the surface normal"b" is the angle of refraction(that thing under the water is the newspaper)L n(normal) \a| \D --------------- |A |.\ | |b'\ |height |--'\*---------- |B C N M